Optical fibers must withstand environmental attack, particularly at flaw sites where chemical weakening progresses rapidly. Particularly harmful are environments of extreme temperature and pressure. Therefore, the fibers must be treated to maintain durability and reliability under such conditions.
Several types of coatings have been utilized in an attempt to protect the fibers from external attack. Various metal coatings were not efficient because they conducted both heat and electricity and failed to provide adequate protection. Plastic coatings did not provide adequate protection against water damage. Ceramic coatings have also been used, but they possess expansion coefficients different from those of the fiber leading to initial strength degradation.
There also appear to be difficulties in adhesions between the fiber coatings and the plastic buffer layer subsequently applied. Bubbles or pockets that result between the coated fiber and buffer may lead to physical degradation of the fiber.
The present invention relates to a method of coating optical fibers with aluminum oxide. The protective layer prevents flaw sites on the glass surface from environmental attack leading to stress corrosion and breakage.